Ghostscript has the clunkiest imaginable syntax, obtuse documentation,
quirky behavior, and poor diagnostics... but it *actually works* unlike
pdftoppm/poppler which gets things wrong.
In this case I observed poppler incorrectly decompresses certain CCITT
encoded monochrome PDFs. So set up Ghostscript to do the job instead.
For the moment this performs monochrome -> RGB conversion via reportlab.
The flag -dUseCIEColor is now deprecated, as it invokes the old engine
which introduces color errors. The new engine requires a PDF/A file
header with hardcoded location of a ICC profile to use, now included in
the project. Portable iterations should generate a PDFA_def.ps based on
the target system; for now OS X with homebrew is presumed.
I have selected sRGB since scanners tend to capture RGB and printing
is not a major consideration for PDF/A.
Also note all file paths given to gs must be absolute. May its creators
be forever haunted for their failure to document this unexpected quirk.
Jim Barlow